This project deals with the molecular mechanisms governing the differentiation of heterocysts, cells specialized for nitrogen fixation, in the filamentous cyanobacterium Anabaena. For this purpose we have cloned and mapped genes coding for the structural components of nitrogenase and nitrogenase reductase; for glutamine synthetase; and for the large subunit of RuBP carboxylase. These cloned genes will be used to study the synthesis and degradation of their respective messages in vivo and as templates for transcription by purified Anabaena RNA polymerase in vitro. Related projects include characterization of proteases active in heterocyst differentiation and attempts to clone their genes.